Field of the Invention
The present invention relates to wireless power transmission.
Description of the Related Art
There is conventionally known a wireless power transmission system including a power transmission device that wirelessly transmits power and a power reception device that receives the power supplied from the power transmission device. In the wireless power transmission system, the power transmission device detects the power reception device present in a power transmittable range through detecting power transmission with small power. Then, authentication processing, based on authenticating power transmission, is executed for the detected power reception device. When the authentication processing is successful, the power transmission device performs charging power transmission, with larger power, for the power reception device (Japanese Patent Application Laid-Open No. 2013-212004). In another known wireless power transmission system, a power transmission device can concurrently transmit power to a plurality of power reception devices.
A power reception device might communicate with a power transmission device different from a power transmission device that is supposed to be its power supply source, when a plurality of power transmission devices is closely arranged and communication ranges thereof overlap one another, in which control information is transmitted and received and communications for wireless power transmission such as the authentication processing are performed.
A case is described where a first power transmission device and a second power transmission device are disposed at positions where their communication ranges overlap one another. A third power reception device is placed on the first power transmission device, while the first power transmission device is transmitting power to a first power reception device and the second power transmission device is transmitting power to a second power reception device.
In such a state, the first and the second power transmission devices have already started the charging power transmission with large power, so that the first and the second power transmission devices cannot perform detecting power transmission. As a result, the third power reception device starts communication connection processing for the authentication processing, when detecting the charging power transmission being performed by the first power transmission device for the first power reception device. In such a case, when the third power reception device broadcasts a message for the communication connection processing, the message is received by each of the first power transmission device and the second power transmission device.
Normally, the second power transmission device does not necessarily have to transmit power to the third power reception device, which is not placed thereon. However, when the message from the third power reception device is received, the second power transmission device might establish communication connection with the third power reception device for performing the wireless power transmission. The second power transmission device might execute the authentication processing with the third power reception device in response to the established communication connection, and set the third power reception device as a target of the power transmission. When the second power transmission device sets the third power reception device that is not placed thereon as the target of the power transmission, inefficient power transmission is performed for the third power reception device.